The present invention relates to an earphone antenna for portable radio equipment which is put on a human body during use, and to portable radio equipment provided with this earphone antenna.
Conventionally, in portable radio equipment to be carried on a human body during use, such as a pager, a radio receiver, an LCD television receiver and the like, a rod antenna or an earphone antenna which utilizes a signal wire for transmitting audio signals to earphones is used as an antenna. For example, such an earphone antenna is disclosed in Japanese Patent Application Publication No. 2003-163529.
In the portable radio equipment which uses a rod antenna and/or an earphone antenna, when put on a human body for use, there has been a problem that because of a significant deterioration of antenna performance when put on the human body, such as in television broadcasts where signals with a large amount of information, e.g., video signals, are processed, a sufficient reception sensitivity cannot be obtained.
In particular, the earphone antenna which utilizes the signal wire for transmitting audio signals to the earphones as an antenna has had a problem that because the earphone and/or the signal wire make direct contact with the human body, the human body has caused a significant influence on the radio equipment via the antenna to substantially deteriorate the stability of reception.
Further, in television broadcasts in Japan, for example, VHF bands from 90 to 108 MHz (1-3 channels), and from 170 to 222 MHz (4-12 channels), as well as the UHF band from 470 to 770 MHz (13-62 channels) are used. Therefore, an LCD television receiver for receiving television broadcasts is required to receive high frequency signals in an extremely wide band range from 90 to 770 MHz. Accordingly, with a conventional rod antenna or earphone antenna, the performance of which is inferior to a fixed-type antenna, it has been extremely difficult to secure a sufficient sensitivity in the required frequency band range.
Still further, because the rod antenna and the earphone antenna are monopole antennas which resonate at λ/4, their reception sensitivity is greatly influenced by the ground size of the portable radio terminal, thereby limiting the design of the portable radio equipment.